Electrical circuit breaker



De.23,1941.` SRHOOD Em, 2,267,463

ELECTRICAL CIRCUIT BREAKER Filed Jan. 29, 1940 INVENTORJ. JTANLEy R,Hoon K EDWARD WLocH gwd Patented Dec. 23, 1941 ELECTRICAL CIRCUITBREAKEI! Stanley B. Hood and Edward W. Bloch, Detroit,

asaignors Mich., Detroit, Mich., a

to W. M. Chaco corporation oi Michigan Company.

Application January 29, 1940, Serial No. 316,166

(Cl. MiO-113) 3 Claims.

This invention relates to an electrical circuit breaker and moreparticularly to an ambient temperature compensated circuit breaker.

It is old to fabricate an electrical circuit breaker from laminatedthermostatic metals such as bimetal or trimetal, having predeterminedamperage ratings, that is to say, the circuit breaker is designed tocarry a given amperage, any excess amperage or overload due to internalresistance heating causing the circuit breaker to react and break thecircuit. Such laminated thermostatic metal circuit breakers must beoperative over a wide range of atmospheric temperatures, for example, acircuit breaker positioned beneath the engine hood of an automobile. Insuch case temperatures from 40 below zero F. to 250 above zero F. areencountered. Thus the problem arises of producing a circuit breakerhaving a given amperage rating which will open and break the circuitupon the passage therethrough of a'given amperage regardless of theatmospheric temperature conditions under which the circuit breaker isoperating. In a bimetal circuit breaker, for example, the high and lowsides expand on a rise intemperature and contract upon a fall intemperature. Thus, unless such a circuit breaker is -compensated forambient temperatures, the circuit breaker would tend to break thecircuit at one amperage at low temperatures and at a lower amperage forelevated temperatures.

Since electrical resistance increases as the temperature increases andfalls as the temperature falls, the electrical resistivity of any givencircuit breaker would vary with the atmospheric temperature conditionsunder which it is operating. Thus, -a circuit breaker calculated to openupon the' passage therethrough of l0 amperes at room temperature, unlessproperly compensated, would break the circuit upon the passage of lessthan l0 amperes as the atmospheric temperature rose.

It is an object of this invention to produce a circuit breaker which iscompensated for variations in the resistivity due to temperature changesso that it will operate to break the circuit at a given amperageirrespective of the atmospheric temperature or the thermal conductivitychanges under which it is operating.

In the drawing:

Fig. 1 is a plan view of the principal form of circuit breaker.

Fig. 2 is a section along the line 2-2 of Fig. l showing the circuitbreaker closed, with a dotted line showing of the position of the armdue to a rise in atmospheric temperature.

Fig. 3 is a vertical section similar to Fig. 2 with 1 cuit breaker armwhen the circuit is broken due to the passage oi an overload or excessamperage through the circuit breaker.

Fig. 4 is a side elevational view similar to Fig. 3 showing the positionot the circuit breaker arm at a lower atmospheric temperature than thatshown in Fig. 3 with the circuit broken in full lines and made in dottedlines.

Fig. 5 is an enlarged section along the line 5-5 of Fig. 1.

Fig. 6 is a plan view of a modified form of circuit breaker.

Fig. 7 is an end view along the line 'I--l of Fig. 6.

Fig. 8 is a side elevation oi the circuit breaker with full line anddotted line showings of the position of the circuit breaker arms atdiierent temperatures, the circuit being made in each instance.

Fig. 9 is a full line showing similar to the dotted line showing of Fig.8 except that the circuit is broken.

Fig. 10 is a schematic showing of the action of the breaker legsincident to a rise intemperature.

Fig. ll is a planview of the circuit breaker showing the compensatingand resistance legs of equal length.

Fig. 12 is a modified form of circuit breaker with the direction ofdeflection of the compensating leg reversed from that shown in theprincipal form of the invention.

Referring more particularly to the drawings the circuit breakercomprises a base I of insulating material provided with posts 2 and 3 towhich the electrical leads or wires 4 and 5 are connected inelectrically conducting relation. A bimetal circuit breaker arm ofhairpin form com prising ambient leg 6 and resistance leg 'I ismountedon post 8 by securing the end of leg 6 to post 8. Post 8 ismounted on the insulating base I. The resistance leg 'I carries anelectrically conducting contact point 9 arranged to make contact withcontact point I0 carried by post 3. An electrically conducting lead I Iis iixed at one end to resistance leg l as at I2 and at the other end topost 2. As shown in Fig. 5, the circuit breaker arm is preferablystamped from an integral piece of'bimetal comprising a high expandinglamina I3 and a low expanding lamina I l. The legs 6 and 1 are connectedby cross piece I5 which acts in the nature of a cooling iin anddissipates heat conducted from the resistance portion of leg 1,

that is, the portion of leg 1 Vbetween connection I2 and post 3.

Since the circuit breaker leg 5, 1 will respond to changes intemperature, it is essential to compensate for this so that the circuitbreaker will break at any temperature upon the passage of any givenamperage through resistance leg 1. To this end it is proposed to makelegs 6 and 1 of different lengths. Where it is desired to have thecircuit breaker break the circuit at any given amperage, say, 10 amperesat temperatures ranging from 40 below zero to 250 F. above zero, itisessential that the leg 6 be longer than the leg 1. If it is desired tohave the circuit breaker break the circuit upon the passage of, say, 20amperes through leg 1 at, say, 0 F., and at 10 amperes at 100 F., thenleg Ii is made shorter than leg 1. If reduction in amperage is notsuiiicient, then direction of deflection of leg 6 is reversed and lengthincreased until the desired drop in amperage required to break thecircuit occurs.

By Way of description rather than limitation, leg 1 is shown longer thanleg 6 and thus the circuit breaker will open at the same current oroverload regardless of the atmospheric temperature within the range oftemperature at which the circuit breaker is designed to operate.

The ambient leg 6 mounted on post 8 controis the pressure with whichcontact 9 bears upon contact I because upon a rise or fall oftemperature the circuit breaker leg bends or ilexes about post 8 as anaxis which is designated X-X, Fig. 1. As the change in temperatureiiexes leg 6, the exing of leg Ii causes leg 1 to swing with and aboutcross piece I5 as an axis. In Fig. 2 the circuit breaker legs 5 and 1are shown in the full lines in the position they assume, say, at 0 F.Leg 1, of course, at all temperatures is under stress so that thecontact 9 presses against contact I0 except when an overload or overamperage is passing through the circuit. As the atmospheric temperaturerises, say, to room temperatureLthe high expanding lamina I3, being onthe underside of the breaker leg 6, and the low expanding lamina I4,being on the upper-side of leg 6, causes the leg 5 to bend upwardlyabout post v8 to the position shown in Fig. 3, full lines, or the dottedline position.' Fig. 2. This swings leg 1 downwardly about cross pieceI5 as a center thus tending to increase the pressure of contact 9 oncontact I0. In other words, as leg 6 curves upwardly, leg 1 remainsapproximately tangent to this curve at the point at which it contactsthecurve, namely, the cross piece l5. This position is illustrateddiagrammatically in Fig. 10. However, leg 1 would only take the positionunder these conditions illustrated in Fig. 10 provided it were not madeof laminated thermostatic metal. However, since leg 1 consists of thesame thermostatic bimetal as leg 6 with the high expanding side down,the rise in temperature simultaneously causes leg 1 to bend or flexupwardly about its support, namely, cross piece I5. This upward bendingof leg 1 counteracts or compensates for the downward swinging of leg 1either with or about cross piece l5 sothat legs 6 and 1 maintain theirsame positions one relative to the other regardless of atmospherictemperature change. Thus, when legs 5 and 1 are of equal length andcontacts 9 and I0 are' positioned on axis X (as shown in Fig. 11), thecontact pressure remains the same atall temperatures.

However, since upon an increase in temperature, the electricalresistivity of leg 1 increases and therefore its rate of heatingincreases, it is essential to compensate for this. To this end leg 1 isextended beyond axis X-X as shown.

`As the leg 6 bends upwardly, Fig. 3, contact 9 tends to swingdownwardly about axis X. However, this downward movement f contact 9 isresisted by contact I0 so that the net result is that as leg 5 swingsupwardly about post 5 the pressure of contact 9 on contact I0 isincreased. The distance that leg 1 extends to the left of post 8, Fig.3, will depend on the length of leg 5 and the contact pressure betweencontacts 9 and I0 desired at any given temperature.

When the circuit is closed as current flows through lead II, leg 1, andlead 5, the temperature of leg 1 rises due to internal resistance and ittends to swing upwardly to the dotted line position, Fig. 3, about crossmember I5 as an axis.-

At an atmospheric temperature. of 0 F. a greater quantity of heat mustbe created in resistance leg 1 to break the circuit than where theatmospheric temperature is, say F. Further, the electrical resistivityof leg 1 at 0 F. is less than at 100 F. so that the same amount of'current passing through leg 1 at 0 F. will generate less heat than thesame amount of, current passing through at 100 F. For this reason at 0F. contact pressure-.between contacts 9 and I0 should be less than at100,F To put it another way, at 0 F. leg 1 shold'beunder less stressthan at 100 F. This exact condition is achieved by arranging ieg 1 sothat it is longer than legG and projects beyond axis X. Thus, as shownin Fig. 2, full lines and in dotted lines Fig. 4, leg 1 is under lessstress at 0 F. than at 100 F., Fig. 3, and the contact pressure iscorrespondingly less so that the same amperage flowing throughresistance leg 1 at 0 F. or at 100 F., for example, will break thecircuit by causing the leg 1 to swing upwardly to the dotted lineposition, Fig. 3, full line position, Fig. 4.

In Figs. 6 through 9 a modii'led form of circuit breaker is showncomprising legs 20 and 2| which are anchored to insulating base 22 byscrews 23, 24. The legs 20 and 2| are made from laminated thermostaticmetal, such as bimetal, positioned on block 22 so that the highexpanding side is on top. Thus upon a. rise in temperature the legs benddownwardly from block 22 as shown in Fig. 9. Leg 20 is made from abimetal having a relatively higher coeilicient of electrical resistivitythan leg 2|. Thus leg 2 0 acts as the resistance leg. Preferably leg 2|is a sumciently good conductor that it willconduct more amperage thanthe amperage rating of theA breaker without an increase in' temperaturedue to internal electrical resistance. The outer end of leg 20 is osetas at 25 and overlies oset 26 inleg 2|. Oisets 25 and 26 carry contactpoints 21. The bimetal legs 20 and 2| are made from thermostatic bimetalhaving substantially the same temperature coefiicients of deflection.Thus at 0 F., for example, the legs 2| will take the position shown inthe full lines, Fig. 8, with contacts 21 engaged and the circuitcompleted through lines 28, leg 20, contacts' and break the circuit. Assoon as the circuit is broken, leg 20 upon cooling tends .to straightenor return to its initial pre-overload position and again make thecircuit. ri`hus leg 20 acts as a resistance leg and leg 2l as an ambienttemperature compensating leg.

If it is desired to have the circuit breaker break the circuit at arelatively high amperage. at a low temperature and at a relatively muchlower amperage at a relatively higher temperature', this can beaccomplished by the modified form shown in Fig. 12. As shown in Fig. 12,the resistance leg 31 is fabricated the same as in the principal form ofthe invention, that is, with the high expanding lamina on the bottom andthe low expanding lamina on the top, but the ambient temperaturecompensating leg 38 has the position of the high and low expandinglamina reversed, that is', the high expanding lamina I3 is positioned ontop and the low expanding lamina I4 on the bottom. Thus as thetemperature rises, the leg 38 will bend or flex downwardly about post 8just the opposite from leg '6, as illustrated in Fig. 3. As leg 38 bendsdownwardly upon a rise in temperature, leg 31 will be swung upwardlyabout cross piece 39 to decrease the contact pressure so that atelevated temperatures a lower amperage will be required to break thecontact. Upon a rise of temperature due to electrical resistance of leg31 and upon a rise in atmospheric temperature, this leg will iiex orbend upwardly about cross bar 39 the same as leg 1.

As is evident from the above, the contact pressure determines thetemperature rise necessary to break the circuit. Thus by varying thecontact pressure one varies the temperature rise necessary to break thecircuit which is the equivalent to changing the amperage rating of thecircuit breaker. By varying the relative lengths of the compensating andresistance legs, the circuit breaker will break the circuit at differentarnperages at different temperatures or at the same amperage atdifferent temperatures, as desired.

We claim:

1. An electrical circuit breaker comprising in combination an integralpiece of laminated therrnostatic metal in the form of a hairpincomprising a pair of legs and an interconnecting cross member, one ofsaid legs acting principally as an electrical resistor and the other legacting principally as an ambient temperature compensating leg, supportmeans for supporting the hairpin shaped member at the end of the ambienttemperature compensating leg, a pair of electrical contacts inelectrical circuit with the resistor leg, one of said contacts beingcarried by the resistor leg at the free end of said resistor leg andmovable relatively away from the 'other contact to break the circuitwhenever an over amperage passes through said resistor leg, each cf saidbreaker legs responding tochange in atmospheric temperature whereby theflexing or bending of the ambient leg compensates for the iiexing orbending of the resistor leg to determine the amperage necessary to breakthe circuit.

2. An electrical circuit breaker comprising in combination a U-shapedmember having its two legs in the form of flat strips of laminatedthermostatic metal, one of said legs acting principally as an electricalresistor and the other leg acting principally as an ambient temperaturecompensating leg, support means for supporting the U-shaped member atthe end of the ambient temperature compensating leg, the said legs beingpositioned side by side with the at side of each leg facing the supportand an edge of one leg facing and spaced from an edge of the other legwhereby the ambient temperature compensating leg is practicallyunaffected by the radiant heat from the resistance leg, a pair ofelectrical contacts in electrical circuit with the resistor leg, one ofsaid contacts being carried by the resistor leg at the free end of saidresistor leg and movable relatively away from the other contact to breakthe circuit whenever an over amperage passes through said resistor leg,each of said breakerlegs responding to change in atmospheric temperaturewhereby the flexing or bending of theambient leg compensates for theflexing or bending of the resistor leg to determine the amperagenecessary to break the circuit.

3. An electrical circuit breaker comprising in combination a U-shapedmember with two legs in the form of flat strips of laminatedthermostatic metal, and an interconnecting cross member, one of saidlegs acting principally as an electrical resistor and the other legacting principally as an ambient temperature compensating leg, supportmeans for supporting the U-shaped member at the end of the ambienttemperature compensating leg, the said legs being positioned side byside with the flat side of each leg facing the supportand an edge of oneleg facing and spaced from an edge of the other leg whereby the ambienttemperature compensating leg is practically unaffected by the radiantheat from the resistance leg, a pair of electrical contacts inelectrical circuit with the resistor ieg, one of said contacts beingcarried by the resistor ieg at the free end of said resistor leg andmovable relatively away from the other contact to break the circuitWhenever an over amperage passes through said resistor leg, each of saidbreaker legs responding to change in atmospheric temperature whereby theflexing or bending of the ambient leg compensates for the liexing orbending of the re sistor leg to determine the amperage necessary tebreak the circuit, said interconnecting cross member having a dependingiiange approximately perpendicular to said legs for preventing saidshaped element from curving transversely and for radiating heat irornthe resistor leg thereby preventing conduction of said heat to theambient les.

STANLEY R. HOOD. EUFJARD W. BLOCH.

